Magnetic device



Sept. 6, 1932. E. s. PRIDHAM 1,876,164

MAGNETIC DEVICE Filed July 1. 1929 20 F D030 v 32 22 I i 2/ 33 I' N N S S J H /3 N I mmvron 28 a: j 2E TTORNEYS.

Patented Sept. 6, 1932 UNITED STATES PATENT "OFFICE EDWIN S. ERIDHAM, OF OAKLAND, CALIFORNIA, ASSIGNOB TO THE MAGNAVOX COM- PANY, OF OAKLAND, CALIFORNIA, A CORPORATION OF ARIZONA MAGNETIC DEVICE Application filed July 1, 1929. Serial No. 375,145.

My present invention relates broadly to a magnetic device of special constructlon, and more particularly to onevsuitable for the reproduction and transmission of sound, wherein the moving parts are made adjustable.

The object of m invention is to provide an improved type of magnetic actuated device for loud speakers, phonograph sound reproducers and the like.

A further object of my invention is to provide in a magnetic device of the above character. means whereby the moving arts and particularly the armature thereo may be adjusted to improve its operation under varying conditions. Other objects and advantages of my invention will be in part evias to provide three magnetic zones or points where a magnetic influence will be exerted upon the three poles of the armature.

In Fig. 1, designates a permanent magnet frame. This frame is shown inthe form of a horseshoe magnet withits north and south poles opposite each other. The upper pole, which is designated by the numeral 11, is of north polarity, and the lower pole, designatedby the numeral 12, is of south polarity. Secured to these two poles there is respectively a, pole piece 13 and a pole piece 14. These pole pieces 13 and 14, it will be understood, are formed of metal having relatively high permeability, and are secured to dent, and in part pointed out more specificalthe ends of the magnetic field structure by ly'in the description taken in connection with any sultable means. the accompanying drawing. 15 are shown for this purpose.

In the drawing I have shown, b way of Extending outwardly at right angles to illustration, only, a preferred em odiment each other, and as a part of the north pole of my invention, and I therefore wish to 'piece 13, there are formed two independent have it understood that the invention is not to or salient poles 16 and 17, and upon the south be limited in any way by these illustrations, pole piece 14 similar independent or salient 5 as it may take various other shapes. 'poles 18 and 19 are formed.- The salient In the drawing, poles 16 and 18 are'arranged so as to project Fig. 1is an enlarged perspective view showoutwardly from the magnet frame 10, and

ing the essential parts of my invention suitparallel to each other, and the independent or table for application to a radio loud speaker, salient poles 17 and 19 are arranged so as to Q or a similar device, project toward each other, and in line with Fig. 2 is a perspective view similar to Fig.

1, showing the manner of adapting my invention to a phonograph sound reproducing mechanism, and v Fig. 3 is a fragmentary pers ective view showing one type of an adjusta le armature supporting means as contemplated by my invention.

A feature which I consider novel is in the sha e of the armature with which I am able to o tain an application of force or an induc-' tive eifect at three points thereupon with a magnetic structure having the usual two poles. In other words, I have provided a three-pole armature which will cooperate with a two-pole magnetic field in a manner that mechanical adjustments thereof can be made and better operation obtained.

. The above is accomplished by providing the two poles of the magnetic field structure the frame 10 so as to provide a relatively narrow air gap between their ends. The

symmetrically in right and lefthand relation with respect to each other upon the poles of the field magnet frame 10.

In this figure of the drawing I also show associated with the electro-magnetic structure above described, a three-pole armature 20. This armature 20, like the salient poles, is of high permeability metal and has a central leg or pole piece 21 which is adapted to be disposed between the salient poles 17 and 19, and to be surrounded by an energizing coil 22, the operation of which will be described in more detail hereinafter.

Projecting from the base of the central pole 21, and upon each side thereof, there are provided oppositely extendin pole pieces 23 and 24. These latter pole pieces 23 and 24 In the drawing, screws pole pieces 13 and 14; may be said to be disposed with polar projections which are arranged so actuated to reproduce sound in a manner well known in the art.

1 In Fig. 2 of the drawing I have illustrated my improved electro magnetic device, as applied to a phonographic sound reproducing 7 device or pick-up. In this illustration it will be noted that several parts of the device are similar in construction and arrangement to that already described, the main outstanding difference being in the provision of a socket or receptacle 28 which is attached rigidly to the armature 20, and in this instance along the center line of the spindle or shaft 25. The socket 28 is arranged to receive a phonograph needle or stylus 29, such as is commonly used in connection with sound records. The stylus 29 is held in place in the receptacle 28 by means of a thumb screw 30. The location of the stylus 29, as shown in this figure of the drawing, is particularly suitable to the wave I type of sound record groove, wherein, as is well known, the needle follows a horizontal and wavy groove upon the record.

If my device, as here constructed, is to be applied to a pick-up for records of the socalled hill and dale type, it will be understood that the socket 28 with its-stylus 29 will be attached to the armature 20 at a point to one side of the spindle or shaft 25, or in other words, in a position similar to the location of the cone attachment shown in Fig. 1.

With a device constructed as is described in connection with Fig. 1 of the drawing, it will be seen that when the armature 20 is properly mounted so that it is freely movable on its pivot 25, its central pole 21 will float freely between the salient poles 17 and 19, and its oppositely projecting poles 23 and 24 will move freely ad acent the salient poles 16 and 18 respectively.

Now, if the coil 22 be energized with a modulated current, so that the polarity of the legs of the armature will be varied in intensity, the armature will oscillate in the magnetic fields adjacent the ends of the salient poles upon the electro magnetic member 10, and in this manner it will cause the cone 26 to vibrate .and thus propagate sound waves. In this instance it will be seen that the armature acts to transmit energy to the cone. The amount and nature of this energy or the magnitude and frequency of the vibrations transmitted will be at all times, .controlled'by the excitation of the coil 22. In

the case of loud speaker actuation, it will beunderstood that the current flowing in the coil 22 will be modulated so as to reproduce the different sound frequencies, as required in the reproduction of music. In other words, the coil 22 when the device is used in connection with a radio, will be connected to the output circuit of the radio amplifier.

When my device is used as a pick-up in connection with phonographically recorded sound waves, the coil 22 will be connected in the in-put circuit of an amplifier tube in a manner well known in the art. With the device thus connected with an amplifier tube and the stylus 29 controlled by a sound rec- 0rd, the armature 20 will be oscillated in the electro magnetic fields adjacent the salient poles of the electro magnetic structure 10 in such a manner that the currents flowing in the coil 22 will be modulated and thus there will be impressed upon the amplifier tube a varying current which will be reproduced in amplified magnitude. This amplified current is then impressed on a telephone receiver or loud speaker for the reproduction of the record.

From the above it will be seen that the ar mature illustrated by me is what is generally termed in the art a balanced type of armature and that my form of construction provides an improvement in balanced arinatures which has long been sought. This improve ment is in the fact that I am able, because of the arrangement, to adjust my armature with respect to the electro magnetic fields in a very satisfactory manner.

Balanced armatures of the prior art types have been mounted between fixed pole pieces arranged on opposite sides thereof, and as these poles are of necessity provided upon permanent magnets and other magnetic structures of rigid construction, it has been impossible to effect any effective adjustment of the armature with respect to the field pieces, or any adjustment between the field poles themselves. \Vith my construction, however, it is possible to secure a large range of adjustment between the armature and the permanently fixed stationary poles of the electro magnetic structure.

One manner of obtaining the above referred to adjustment of the armature with respect to the magnetic polesis illustrated in Fig. 3 of the drawing. In this illustration the spindle '25 is shown as journalled in a cradle or yoke 31. The yoke or cradle 31 is,in turn shown as supported upon an ad- 'u'stable screw 32, which projects through a suitable threaded support 33. It will be understood that the cradle or support 31 may have an additional supporting means, as for instance, a guideway in which it might freely move in the direction of movement provided by screw 32. With a mounting of this type it will be readily seen that thearent north 'pole 16, and the free end 24 of mature 20 may be moved toward and away fgom the poles ofithe electro magnetic frame 1 The operation of-my improved device may be explained as follows:

Referring first to the loud speaker arrangement illustrated in Fig. 1, and assuming that the coil 22 is at the instance so energized that the central ole 21 is north at its free end, and the po cs 23 and 24 are south, it will then be seen that the armature will tend to mox'ein a clock-wise direction, the free end of the pole 21 being attracted by the salient south pole 19, the free end of the armature leg 23 being attracted by the salithe armature 20 being repelled by the salien south pole 18. At this instant, it will be seen that two legs of the-armature 20 will be attracted and one of the legs repelled, and

with this arrangement it will also be seen that the combined force of this attraction and repulsion will be cumulative and applied in unison, so that a maximum of force may be said to be exerted by the magnetic field upon the armature 20.

An explanation of the above assumed polarity of the projecting arms 23 and 24 of the armature 20 is not thought to be necessary, but for the purpose of clearness, it will be stated that since the coil 22 determines the polarity of the armature 20, it will be readily appreciated that the south pole end of the winding 22 will be opposite that of the north pole and, as a result, in the assumed situation the flux will divide at the south pole end of the winding, and thus provide two south oles as indicated 1n the drawing. It will e understood, however, that these polarities may alternate or change from one intensity to another as the excitation of the coil 22 is varied.

With reference now to the arrangement illustrated in Fig. 2 it will be assumed that the same polarities as suggested above, exist in the armature 20. With this arrangement, as the armature 20 is oscillated? in the magnetic fields adjacent the salient poles of the electro magnetic field structure 10, the flux therethrough will var and thus induce varying currents in the C011 22 which, when properly detected and amplified, will be suitable for the actuation of a telephone re-. ceiver or loud speaker.

-With the arrangements above described it will be appreciated that the characteristics of the coil 22 can not be conveniently changed and it is for this reason that I have provided the adjustable features in connection with my armature as above related. This mechanical feature is'well illustrated in Fig. 3 of the drawing, and since its operation is mechanical and of a relatively simple nature, it is thought that no further explanation as to its operation is necessary. It willbe sufficient to say thatas the screw 32 is turned the armature 20 may be moved toward and away I of each of the gaps adjacent the salient poles 17 and 19, are formed in series with the air gaps adjacent the poles 16 and 18, it will be readily appreciated that the magnetic reluctance of the complete circuits will be effectively varied by an adjustment of the armature 20 in the manner disclosed.

While certain features of the present invention are more or less specifically described, I wish it understood that various changes may be resorted to without departing from the spirit of my invention as defined in the appended claims, similarly, that the materials and finishes of the several parts employed may be such as the manufacturer may decide, or varyingconditions or uses may demand.

Having thus described my invention, what I claim and desire to secure by Letters Patent is 1. A magnetic actuating mechanism for sound transmission devices and the like comprising a magnetic field producing element having a pair of polar projections formed upon each pole thereof and disposedto provide two magnetic flux paths from each pole,

a pivoted three pole balanced armature adapted to magnetically co-operate with said polar projections, and a winding on said armature.

2. A magnetic actuating mechanism for sound transmission devices and the like comprising a magnetic field producing element armature associated with said magnet adapted to magnetically co-operate with said poles at three points.

4. In a sound re roducing and transmitting device, the combination of a magnet provided with pole pieces disposed in pairs to provide paths of magnetic flux disposed at an angle to each other, and a freely pivoted three ole armature associated with said magnet a apted to magnetically co-operate with said poles at three points.

5. A magnetic actuating mechanism for sound transmission devices andthe like comprising a magnetic field producing element having a pair of poles of similar polarity formed upon each pole thereof extending at an angle to each other in the same plane,

and a three pole armature adapted to mag- 'magneticfield producing element, a three pole armature adapted to magnetically cooperate with said pairs of poles at three points, and means for adjusting the position of said three pole armature with respect to said poles to vary the magnetic coupling.

7. A magnetic device for sound transmis sion and like purposes comprising a two pole magnetic structure having polar projections at each pole extending at right angles to each other and disposed in the same plane, and a three pole armature having one of its poles located between two of said polar projections and its remaining poles adjacent the other polar projections.

8. A magnetic device for sound transmission and like purposes comprising a two pole magnetic structure having polar projections at each pole extending at right angles to each other and disposed in the same plane, a magnetically balanced, three pole armature having one of its poles located between two of said polar projections and its remaining poles adjacent the other polar projections, a winding upon one of the poles of said armature, and an adjustable support for said armature whereby it can be moved with respect to said magnetic structure without changing the magnetic balance thereof.

9. A magnetic actuating mechanism for sound transmissiondevices and the like, comprising a magnetic field producing element having a pair of polar projections formed upon each pole thereof and disposed symmetrically with respect to said field producing element, and a pivoted three pole armature adapted to magnetically cooperate with said polar projections at three points.

10. A magnetic actuating mechanism for sound transmission devices and the like, comprising a magnetic field producing element, a pair of poles extending at an angle to each other secured to each pole symmetrically in right and left hand relation upon said field producing element, and a pivoted three pole armature adapted to magnetically cooperate with said poles.

11. A magnetic actuating mechanism for sound transmission and the like, comprising a magnetic field producing element having a pair of poles of similar polarity formed upon each pole of the magnetic field producing element and extending at an angle to each other, said poles being disposed symmetrinetically cooperate with said poles at three points, and means for adjusting the position of said armature to vary its distance from 70 one of the poles of each pair.

EDWIN S. PRIDHAM. 

